The generation of high frequency signals has become extremely important due to the increasing use and application of wireless technology and high frequency devices such as personal digital assistants (PDAs) and mobile phones. Currently, several methods and devices can be used to generate high frequency signals. One example is an oscillator, which produces a signal that resonates or vibrates at a specific frequency. There are several types of oscillators. Oscillators can be mechanical, electrical, or a combination of the two, namely electro-mechanical, in nature. Electro-mechanical oscillators are commonly used because of their ability to generate a stable signal at a precise frequency. An electro-mechanical oscillator uses the vibrations of a mechanical element to create an electrical signal. Electro-mechanical oscillator signals are often used in applications involving timers due to the precise and stable nature of the generated signal. Electro-mechanical oscillators used in timing applications are often referred to as timing oscillators.
Timing oscillators can be used in several devices including digital clocks, radios, computers, oscilloscopes, signal generators, and cell phones. Timing oscillators generate a clock signal, for example, as a reference frequency to help synchronize other signals that are received, processed, or transmitted by a device. Often times, multiple processes are run simultaneously on a device and the execution of such processes rely on a clock signal that is generated by the timing oscillator. A designer's or user's ability to effectively manage and synchronize data at high speeds using timing oscillators makes electro-mechanical oscillators a valuable component of several hardware and software designs and devices.
An example of an electro-mechanical timing oscillator is a crystal oscillator. When an electric field is applied to a crystal, the crystal becomes distorted. Upon removal of the electric field, the crystal returns to its previous shape and generates an electric field and voltage. This phenomenon is known as piezoelectricity. Depending on the composition of the crystal, the signal produced by the crystal will have a certain resonant frequency. However, using a crystal oscillator for high frequency applications may have several disadvantages. The resonant frequency of the signal generated from a crystal oscillator is dependent on the size and shape of the crystal. Most crystal oscillators are useful for generating signals in the KHz to MHz range whereas most of the latest technology demands signals in the GHz range. Furthermore, the size of a crystal is significantly large occupying more space on a chip compared to other available components.
One solution to overcome the limitation of the generated frequencies of a timing oscillator is to use multipliers. The generated signal can be multiplied using a mixer or a number of other devices known to one of skill in the art to output a new signal at a much higher frequency. For example, a multiplier receiving a signal with a frequency of 50 MHz as an input, can output a final signal of 2 GHz by multiplying the input signal by a factor of 40. However, such an approach is problematic, since doubling a signal's frequency may result in increasing the phase noise, for example, by 6 dB. Hence converting a signal from the MHz range to the upper MHz range or GHz range will result in a significant corruption of the signal quality because of an increase in the phase noise. Conventional timing oscillators may thus not be ideal for generating high frequency signals.